Structures of thePorphyromonas gingivalisOxyR regulatory domain explain differences in expression of the OxyR regulon inEscherichia coliandP. gingivalis

OxyR transcriptionally regulatesEscherichia colioxidative stress response genes through a reversibly reducible cysteine disulfide biosensor of cellular redox status. Structural changes induced by redox changes in these cysteines are conformationally transmitted to the dimer subunit interfaces, which alters dimer and tetramer interactions with DNA. In contrast toE. coliOxyR regulatory-domain structures, crystal structures ofPorphyromonas gingivalisOxyR regulatory domains show minimal differences in dimer configuration on changes in cysteine disulfide redox status. This locked configuration of theP. gingivalisOxyR regulatory-domain dimer closely resembles the oxidized (activating) form of theE. coliOxyR regulatory-domain dimer. It correlates with the observed constitutive activation of some oxidative stress genes inP. gingivalisand is attributable to a single amino-acid insertion inP. gingivalisOxyR relative toE. coliOxyR. Modelling of full-lengthP. gingivalis,E. coliandNeisseria meningitidisOxyR–DNA complexes predicts different modes of DNA binding for the reduced and oxidized forms of each.